I had the same problem after running continuously for 16 hours. Tried alt tab / ctrl alt delete as well but the program refused to give up the focus. Thought maybe it might just be slow shutting down. Let it sit and went to bed. When I got up this AM it would give up enough focus to show the alt tab menu but refused to shut down or actually let the focus pass to a program other than the alt tab menu or task manager. Was able to restart the system through the task manager and everything seems ok now.
My system stats:
Operating System: Windows 10 Home 64-bit (10.0, Build 14393) (14393.rs1_release_inmarket.161004-2338)
Language: English (Regional Setting: English)
System Manufacturer: HP
System Model: 750-170se
BIOS: A0.08
Processor: Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz (8 CPUs), ~3.4GHz
Memory: 49152MB RAM
Available OS Memory: 49088MB RAM
Page File: 3651MB used, 52604MB available
Windows Dir: C:\WINDOWS
DirectX Version: DirectX 12
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
Miracast: Available, with HDCP
Microsoft Graphics Hybrid: Not Supported
DxDiag Version: 10.00.14393.0000 64bit Unicode
--------------
Display Devices
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Card name: NVIDIA GeForce GTX 960
Manufacturer: NVIDIA
Chip type: GeForce GTX 960
DAC type: Integrated RAMDAC
Device Type: Full Device
Device Key: Enum\PCI\VEN_10DE&DEV_1401&SUBSYS_2B4D103C&REV_A1
Device Status: 0180200A [DN_DRIVER_LOADED|DN_STARTED|DN_DISABLEABLE|DN_NT_ENUMERATOR|DN_NT_DRIVER]
Device Problem Code: No Problem
Driver Problem Code: Unknown
Display Memory: 26560 MB
Dedicated Memory: 2016 MB
Shared Memory: 24543 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: S24B300
Monitor Id: SAM08CC
Native Mode: 1920 x 1080(p) (60.000Hz)
Output Type: HDMI
Driver Name: C:\WINDOWS\System32\DriverStore\FileRepository\nvhdcwu.inf_amd64_16f6c9b501baeb7d\nvd3dumx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvhdcwu.inf_amd64_16f6c9b501baeb7d\nvwgf2umx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvhdcwu.inf_amd64_16f6c9b501baeb7d\nvwgf2umx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nvhdcwu.inf_amd64_16f6c9b501baeb7d\nvwgf2umx.dll
Driver File Version: 21.21.0013.6909 (English)
Driver Version: 21.21.13.6909
DDI Version: 12
Feature Levels: 12_1,12_0,11_1,11_0,10_1,10_0,9_3,9_2,9_1
Driver Model: WDDM 2.1
Graphics Preemption: DMA
Compute Preemption: DMA
Miracast: Not Supported by Graphics driver
Hybrid Graphics GPU: Not Supported
Power P-states: Not Supported
Driver Attributes: Final Retail
Driver Date/Size: 7/31/2016 8:00:00 PM, 17799424 bytes
WHQL Logo'd: Yes
WHQL Date Stamp: Unknown
Device Identifier: {D7B71E3E-5741-11CF-7169-400B1BC2D835}
Vendor ID: 0x10DE
Device ID: 0x1401
SubSys ID: 0x2B4D103C
Revision ID: 0x00A1
Driver Strong Name: oem149.inf:0f066de3b391ac9a:Section092:21.21.13.6909
ci\ven_10de&dev_1401&subsys_2b4d103c
Rank Of Driver: 00D10001